1. Field of the Invention
The present invention relates to a relay control circuit, and in particular, to a relay control circuit which can prohibit the input of an operation signal of a relay, which supplies power to a load such as a motor, for a certain period of time while the load is not driven (standby state).
2. Related Art
In a relay control circuit which controls the driven state and the non-driven state of a load such as a motor by turning a relay on and off (e.g., a circuit which can control the driven state and the non-driven state of a motor for driving a window glass in a power window apparatus by turning a relay on and off), if a foreign object becomes caught by the window glass while the motor is being driven, the movement of the window glass is obstructed by the foreign object. In order to prevent damage to the foreign object and the drive system which may be caused in such a case, a function may be added which detects an overloaded state of the motor by use of motor current or the like, and when an overloaded state is detected, the catching of the foreign object which stops the driving of the motor is detected and prevented. Window glasses at the front passenger's seat and the rear passengers' seats can be operated not only by respective operating switches for the seats, but also by a operating switch (master switch) provided at the driver's seat. Therefore, even if a power window controller detects the catching of a foreign object by the window glass, there is the concern that an operation switch may be operated again. Here, it may be desirable to prohibit the input of the relay signal for a certain period of time in order to maintain the non-driven state of the load. Further, in power antenna devices, power pole devices and the like, because a moving portion is provided in a place which is difficult for the operator to monitor, it may be desirable in these cases as well to prohibit the input of a relay operation signal for a certain period of time.
When it is desired to prohibit, for a certain time, the input of the operation signal of the relay which drives the load (for example, in a circuit using two relays to control the forward rotation/reverse rotation of a motor which is a load), an input prohibiting function of the relay control circuit is operated, i.e., a function which simultaneously switches the two relay contacts to the power source side so that voltage is applied in the directions of forward rotation/reverse rotation. In this way, the load is not driven, and the input of the relay operation signal, such as a switch input or the like, can be prohibited for a certain period of time. However, in order to operate this input prohibiting function, it is necessary to supply power to the relay control circuit, which limits the reduction of the amount of power consumed.
In a circuit which applies voltage in one direction to a motor, which is a load, by using one relay, if the circuit is structured such that power is supplied to a relay control circuit via the relay, a circuit structure in which almost no power is consumed while the load is not driven can be realized. However, in such a case, because power is not being supplied to the relay control circuit as well while the load is not being driven, it is difficult to maintain the input prohibiting function which prohibits input of the relay operation signal to the relay control circuit for a certain time. Accordingly, in this case, in order to operate the input prohibiting function of the relay control circuit, it is necessary to supply power to a portion or to all of the relay control circuit even when the load is not driven.